Conventionally, according to ultrasonography using an ultrasound diagnosis apparatus, contrast enhanced ultrasonography of taking an contrast enhanced image that is imaged of a blood flow with high sensitivity is performed by enhancing a blood flow signal with an ultrasound contrast agent of which main component is microbubbles (for example, see “Medical Image/Radiological Equipment Hand Book” edited by Japan Industries Association of Radiological Systems, published by Nago Bijutsu Insatsu Kabushiki Kaisha, 2001, pp. 221-225).
In a contrast enhanced ultrasonography of the abdomen of which object is a screening diagnosis on “benignancy and malignancy” of a hepatic tumor, it is recommended to evaluate contrast enhanced images taken in two phases, which are explained below, after giving a subject an ultrasound contrast agent that can be injected into a vein.
A first phase is a phase called an arterial phase or a blood-vessel early phase. The blood-vessel early phase corresponds to a period from an injection of an ultrasound contrast agent until several tens of seconds later, which is a phase in which an arterial blood flow can be dynamically observed owing to the injected ultrasound contrast agent.
Because a malignant hepatic tumor is mainly dominated by an artery, a doctor can confirm a structure of a blood vessel that nourishes a hepatic tumor by referring to a contrast enhanced image in a blood-vessel early phase. Particularly, in order to evaluate dynamics of the blood flow to the hepatic tumor, the doctor refers to an animated image of contrast enhanced images in the blood-vessel early phase by using an animation display function of the ultrasound diagnosis apparatus.
A second phase is a phase called a parenchymal phase or a late phase. The late phase corresponds to a period after approximately five minutes from an injection of a ultrasound contrast agent (after approximately four minutes in some facilities), which is a phase in which a distribution state of the ultrasound contrast agent remaining in the liver can be observed in a state that the ultrasound contrast agent in a blood flow is sufficiently reduced by pulmonary circulation.
It is known that a normal hepatic cell is dominated by a portal vein, in contrast to a malignant hepatic tumor, which is dominated by an artery as described above. Moreover, a normal hepatic cell includes a flow route of a blood flow in a fine structure, and additionally includes a macrophage that is called a Kupffer cell. By contrast, a malignant hepatic tumor loses a fine structure and a Kupffer cell that a normal hepatic cell has, in order to construct a unique tissue structure.
For this reason, the ultrasound contrast agent is taken by a macrophage into a normal hepatic tumor, in contrast, a degree of an intake of the ultrasound contrast agent into a malignant hepatic tumor is low. As a result, a high brightness part on a contrast enhanced image taken in the late phase is basically a signal obtained from a normal hepatic tumor. Therefore, the doctor can clearly observe the form of a hepatic tumor, by referring to the contrast enhanced image in the late phase. Particularly, in order to confirm a distribution of hepatic tumors, the doctor refers to a still image of the late phase that statically indicates a distribution of the ultrasound contrast agent, or a stereoscopic still image when using an ultrasound probe that can three-dimensionally scan with ultrasound.
Recently, in addition to screening a hepatic tumor, planning of an appropriate treatment course by diagnosing the malignancy (differentiation) of a hepatic tumor is desired. In such case, the doctor diagnoses the malignancy of a hepatic tumor by observing whether an inflow position of an artery in a contrast enhanced image taken in the blood-vessel early phase reaches the inside of the tumor or concentrates in a marginal region of the tumor, with respect to the hepatic tumor part that is a low-brightness part in a contrast enhanced image taken in the late phase.
For this reason, according to a conventional ultrasound diagnosis apparatus, as shown in FIG. 14, an animated image of contrast enhanced images taken in an arterial phase and a still image of a contrast enhanced image taken in an late phase are displayed in parallel, and the doctor observes the parallel-displayed contrast enhanced images, thereby performing screening of hepatic tumor and diagnosis of the malignancy. FIG. 14 is a schematic diagram for explaining the conventional technology.
However, contrast enhanced images in the blood-vessel early phase and the late phase displayed by the conventional ultrasound diagnosis apparatus are not always in the same cross section, and it is difficult to grasp precisely to which position in the tumor the artery invades because of parallel-display, the doctor cannot perform screening of hepatic tumor and diagnosis of the malignancy with precision.
To perform screening of hepatic tumor and diagnosis of the malignancy with precision, recently, reported is a “Re-Injection” method of by which after an ultrasound contrast agent is given at first time, and when reaching a late phase, the ultrasound contrast agent is then again given at the second time, a contrast enhanced image is taken on which an ultrasound contrast agent distribution in the arterial phase is newly displayed as superimposed over an ultrasound contrast agent distribution in the late phase.
However, according to the “Re-Injection” method described above, even though screening of hepatic tumor and diagnosis of the malignancy can be performed with precision, there is a problem that a physical burden onto a subject body and an operational burden onto a doctor increase because an ultrasound contrast agent is given twice, and an examination efficiency worsens because an examination time is extended.